Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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580 FXUS62 KRAH 211759 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 155 PM EDT Sat Oct 21 2017 .SYNOPSIS... High pressure will extend across the Carolinas through Sunday. A strong cold front will approach from the west Monday, and cross central NC on Tuesday. && .NEAR TERM /THROUGH TONIGHT/... As of 1005 AM Saturday... High pressure at the surface and aloft will remain in control of the weather through tonight across central NC. Aside from some passing cirrus, expect sunny skies and mild afternoon temperatures. Temps will average 8-10 degrees above normal for late October, ranging between the upper 70s-lower 80s. The sfc ridge associated with the high will drift offshore tonight through early Sunday. The resultant sely low level flow will advect enough warm moist air to produce patchy fog over sections of the coastal, plain, Sandhills, and potentially the eastern Piedmont by daybreak Sunday. Not expecting dense fog, so no travel issues anticipated. It will be a bit milder with low temps in the upper 40s to around 50 nw to the low-mid 50s southeast. && .SHORT TERM /SUNDAY AND SUNDAY NIGHT/... As of 355 AM Saturday... The mid-upper ridge in the vicinity of the coast of the Carolinas, and the associated surface ridge axis extending swwd into the sern US, will move little through the weekend. Persistence will still largely rule, although another day`s worth of ely low level flow around the ridge will have allowed surface dewpoints to climb more solidly into the 50s, to around 60 degrees or so in the Sandhills and srn Coastal Plain, by Sun evening. This will favor both slightly higher RH values than recent days, and also (mostly) few-scattered stratocumulus midday onward. Bufr forecast soundings from both the NAM and GFS suggest this stratocumulus may become broken in coverage/mostly cloudy by late afternoon-evening over srn portions of the RAH forecast area. Cloud cover, including some low clouds and fog centered again over ern portions of the forecast area, will further increase into the mostly cloudy range overnight, but the continued presence of a capping inversion aloft and lack of deep moisture, suggest conditions will remain dry. && .LONG TERM /MONDAY THROUGH SATURDAY/...
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As of 155 PM Saturday... Model consensus has improved greatly concerning the cutting off of a vigorous short wave moving into the Tennessee Valley Sunday night. This short wave subsequently lifts northeast into the Ohio Valley as it is absorbed into a stronger long wave trof which will be digging deeply into the eastern CONUS through midweek. A strong cold front associated with the lead short wave will move into the mountains early Monday, and race east across central NC during the afternoon and evening. Low level flow increases dramatically and very quickly ahead of this stacked system, with southerly low level jetting exceeding 35Kt by midday providing a deep surge of moisture (PW`s rapidly approaching 2.0 inches) ahead of the surface front. This initial surge of low level moisture and warm air advection will likely produce a pre- frontal QLCS, which would develop and move into the southwest Piedmont by early afternoon. The low level jetting continues to strengthen, with H85 winds exceeding 50 knots as the initial line of convection moves across central NC, and will likely be followed by another line of convection accompanying the surface front a couple of hours later. Instability will be unimpressive and somewhat of limiting factor, but the low level forcing/convergence and upper diffluence assoicated with the short wave lifting north of the area will be very strong. Damaging wind gusts could accompany stronger storms, and the strongly sheared low level profile would support rotating storms, so a tornado or two look to be possible. Will transition categorical PoPs across the area from 18-06Z, with a 6- hour window of 90% PoPs area-wide centered around 00Z tomorrow evening. Warm air advection will partially offset increasing cloudiness and highs will reach the low 70s west to near 80 in the southeast. The convective zone will move rapidly east of the area after midnight, with clearing and weak initial cool air advection over at least the western half of the area by sunrise. Mins will be mostly in the lower 60s, with some upper 50s in the west. Drier and cooler air will be filtering into the area on Tuesday, with potentially some instability showers across the northern tier as the main upper trof rotates across the Ohio Valley. Highs Tuesday will be mostly in the upper 60s to lower 70s, with further cooling into the low and mid 60s for Wednesday through Thursday. Mins will bottom out Wednesday night as the upper trof axis shifts east of the area and the drier aimass cools under better radiational conditions. Some climatologically cooler locations will fall to the upper 30s, with widespread lower 40s elsewhere. Shortwave ridging and return flow as surface high pressure moves offshore will give us a warmup late in the week, with highs Friday and Saturday mostly in the mid 60s to lower 70s.
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&& .AVIATION /18Z SATURDAY THROUGH THURSDAY/... As of 140 PM Saturday... There is a high probability that VFR conditions will persist across central NC through 00Z Monday as high pressure at the surface and aloft controls the weather across central NC. The exception will be after 04Z tonight as patchy fog will develop, likely reducing the visibility into the MVFR range, particularly in vicinity of KRWI and KFAY, and possibly at KRDU. Pockets of IFR/LIFR visibility may occur close to daybreak in proximity of KRWI. Pockets of fog will disperse within an hour or sunrise. The good aviation conditions are expected to persists through early Sunday evening. Later Sunday night and on through Tuesday, an approaching frontal system will draw a moist low level air mass into central NC leading to an increased threat for sub VFR ceilings as well as increasing coverage of showers and a few thunderstorms, especially late Monday through early Tuesday. A return to VFR parameters anticipated for Tuesday night through Thursday. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...WSS NEAR TERM...WSS SHORT TERM...MWS LONG TERM...mlm AVIATION...WSS is the U.S. government's official web portal to all federal, state and local government web resources and services.